I'm not sure you actually did make a bad choice. You just can't expect a low power laptop to perform like a high power desktop.
Your GTS is one of those 'nicer cards'. There isn't anything that's really much better out there.
Laptop 3DMark05 scores:
GeForce GTX 260M =14773
Radeon HD 5850 = 15829
GeForce GTS 360M = 16628
Radeon HD 5870 = 17932
GeForce GTX 285M = 18935 ~+12%
GTX 285M SLI = 21611
If you are highly skilled (and lucky) you could might be able to upgrade your video card yourself.
You could buy a
GTX 285M MXM module for $485
The skill and luck parts come into play because you'll need to disassemble the laptop, install the module and get the heatpipe cooler re-installed correctly. Usually you don't see that kind of maintenance outside of a factory authorized repair facility.
That $485 upgrade would get you about 12% better performance.
Even the top end Laptop stores that do custom builds don't offer anything more than GTS 360M on the G51Jx-A1.
G51Jx-A1 upgrade options @ ExoticPC
If the GTS 360M isn't cutting it for you - about your best option would be to return the laptop and get a better model. Or a desktop PC.
I've heard that Clevo is getting ready to
make SLI GTX 470 laptops. Prepare yourself for some sticker shock though.